Ferroelectric fluorinated copolymers with improved adhesion properties
Résumé
Modified fluorinated electroactive poly(VDF-co-TrFE) copolymers with improved adhesion properties,
on glass or metal substrates, are presented. Vinylidene fluoride (VDF) and trifluoroethylene (TrFE) were
terpolymerized with 1 to 8 mol% of 2-(trifluoromethyl)acrylic acid (MAF) as an adhesion-promoting
monomer. Monitoring the evolution of the reactor pressure and of the 19F NMR spectra of the terpolymer
over the course of solution polymerization revealed the very pronounced compositional heterogeneity of
the resulting terpolymer. The terpolymerization was scaled-up and implemented under aqueous suspension
conditions in a 3 L-autoclave. This aqueous process, more industrially viable, was successful in spite
of the undesirable addition reaction of water onto MAF producing 3-hydroxy-2-(trifluoromethyl)propanoic
acid. The structure of the resulting polymers was characterized in detail by 1H, 19F NMR and FTIR
spectroscopies, and their physical properties (thermal, adhesion and electroactive) were examined. The
decarboxylation of MAF, observed by TGA to occur at ca. 250 °C, is not a limitation for the targeted applications.
A MAF content of 1 mol% was shown to be sufficient to provide very good adhesion onto glass
and metal substrates, and also to decrease the water contact angle from 104° (reference poly(VDFco-
TrFE) copolymer) to 86° (terpolymer containing 1 mol% of MAF). Polarization studies revealed that the
terpolymers exhibited identical ferroelectric behavior as unmodified poly(VDF-co-TrFE) copolymers,
characterized by a wide hysteresis (Ec = 60 MVm−1) and a high saturation polarization (Psat = 77 mC m−2).
This study reports the first electroactive fluorocopolymers with improved adhesion, and paves the way
for better incorporation of fluorinated electroactive thin films in multilayer films for flexible electronic
devices.